The present invention relates to a highly flexible process for the substantially complete recycling and reutilization of waste of various composition, and in particular of solid urban waste, which allows a final recovery of combustible substances and of amending and/or fertilizing substances.
As is known, the main consequence of the development and constant growth of mass consumption is the enormous and constantly increasing production of waste in general and of solid urban waste in particular.
The problem of the disposal of these enormous amounts of waste is currently managed with various methods, one of which consists in permanently or temporarily abandoning the waste, and in particular solid urban waste, in controlled landfills in view of a future total or partial reutilization, such landfills being meant to protect the inhabitants of the surrounding areas against air and water pollution; other methods consist in disposing solid urban waste by means of a bacterial aerobic process termed composting. This process is essentially a biological oxidation similar to that which spontaneously occurs in nature in the undergrowth due for example to the presence of macerated leaves or the like; it is therefore an intrinsically slow process which can, however, be made faster and more complete by trying to aerobically facilitate the transformation of the organic substances, utilizing the enzymes secreted by the microflora which is naturally associated with said organic substances; in this process it is possible to partially improve the organic part of solid urban waste by treating the organic material with the sludge produced by urban conditioning plants.
Another known method consists in incinerating solid urban waste with energy recovery, i.e. a process of complete pyrolysis of the waste which produces both gaseous effluents, which can be used to produce energy and must be subsequently conditioned before they are sent to the chimney, and solid effluents to be sent to the slag discharge.
These known disposal methods for solid urban waste in practice entail the use of plants which are complicated, expensive and difficult to manage, especially due to the fact that the composition of solid urban waste may vary even to a considerable extent and also due to the fact that the energy yield does not always justify plant and production costs. The effluents produced with current plants, especially incineration plants, furthermore have a high pollution rate and require adequate elimination plants.
In order to optimize known methods for solid urban waste recovery, it has already been proposed to separate the combustible part therefrom and to use only this part as waste-derived fuel; in this case the solid urban waste is processed so as to separate the ferrous and non-ferrous metallic parts, the glass and inert materials and thus obtain an entirely combustible part as residual. The adopted separation devices produce fuels with low heating value which are subsequently enriched; said devices are usually arranged ahead of the incineration furnace. If the fuel obtained as described above is instead ground to homogenate the mass, the resulting fuel has a higher heating value. In order to allow the storage of fuel derived from solid urban waste, said fuel is furthermore pelletized, for example by extrusion.